An alternator for a vehicle is known from the document EP-0 762 617 A1, and comprises pole pieces having poles in the form of interlaced claws, and inter-pole permanent magnets interposed between the adjacent claws. The magnets reduce the leakages of magnetic flux and contribute to reinforcing the magnetic flux. When the manufacturing tolerances of the pieces are made relatively wide in order to reduce costs, an inter-pole magnet may break under the effect of the centrifugal forces and the considerable heating engendered by the rotation of the rotor at high speed (opening of the pole horns).
One object of the invention is to supply an alternator allowing the magnets to be fixed while reducing the risk of breaking the magnet, without requiring very fine manufacturing tolerances.